Numerical and experimental modelling of gas flow and heat transfer in the air gap of an electric machine. Part II: Grooved surfaces

Abstract

The study deals with the cooling of a high-speed electric machine through an air gap with numerical and experimental methods. The rotation speed of the test machine is between 5000~40000 r/rain and the machine is cooled by a forced gas flow through the air gap. In the previous part of the research the friction coefficient was measured for smooth and grooved stator cases with a smooth rotor. The heat transfer coefficient was recently calculated by a numerical method and measured for a smooth stator-rotor combination. In this report the cases with axial groove slots at the stator and/or rotor surfaces are studied. Numerical flow simulations and measurements have been done for the test machine dimensions at a large velocity range. At constant mass flow rate the heat transfer coefficients by the numerical method attain bigger values with groove slots on the stator or rotor surfaces. The results by the numerical method have been confirmed with measurements. The RdF-sensor was glued to the stator and rotor surfaces to measure the heat flux through the surface, as well as the temperature.

Optimising the refrigeration cycle with a two-stage centrifugal compressor and a flash intercooler

“…The articles written by Kuosa et al (2004Kuosa et al ( , 2005 could be used as an alternative source.…”

Multi‐physics design of a novel turbine permanent magnet generator used for downhole high‐pressure high‐temperature environment

“…However, the convection heat transfer coefficient (CHTC) used in lumped-parameter thermal-network analysis and finite element analysis (FEA) is most often based on empirical formulations and convection correlation which is not suitable for complex structures and special working conditions [12]. With the increased computing power, computational fluid dynamics (CFD) is increasingly used in the calculation of fluid distribution and CHTC [13][14][15][16]. Always, the average surface CHTC from the CFD is utilised in the following thermal analysis rather than the uneven surface CHTC in fact, which will produce calculation errors to some extent.…”

Multiphysics thermal design of a high-speed permanent-magnet machine

“…In [1], a numerical thermal analysis of a conventional induction machine is done but the coefficients of thermal convection are calculated by empirical equations. In [2] and [3], an extensive numerical CFD approach for estimation of the turbulent fluid properties in the air gap in a high-speed induction machine is reported. The temperature rise of the fluid and the local coefficient of thermal convection in the air gap are determined and experimentally validated, but the temperatures of stator and rotor outer surfaces are accepted as constant values without estimation of the temperature distribution in the solid domain of the machine.…”